1. Field of the Invention
The present invention relates to an enclosure for audio loudspeakers, and more particularly, to an improved enclosure which resonates across a low frequency band to enhance low frequency sound reproduction.
2. Discussion of the Prior Art
Loudspeaker enclosures are generally well known. Typically, various loudspeaker and enclosure combinations are used to reproduce music as part of a home or commercial audio entertainment system. At low frequencies, i.e., less than 250 Hz, it is known that direct radiating loudspeakers tend to be omnidirectional, producing soundwaves from the front and back of the loudspeaker which are of equal intensity, but opposite phase. The forward and backward traveling soundwaves thus interfere destructively, reducing effective power output and reducing the volume of sound produced at those frequencies.
This problem can be solved through the use of a baffle, and an enclosure for the loudspeaker acts as a baffle. The backward traveling soundwaves are bounced off the back surface of the enclosure to interfere constructively, rather than destructively, with the forward traveling soundwaves. Thus, increased power and efficiency result from a well designed baffle. However, since wavelength is inversely proportional to frequency, a relatively large volume enclosure is required at low frequencies.
The use of baffles introduces another problem. The resulting enclosure is subject to developing resonance at one or more frequencies. This resonance increases power output at the resonating frequencies and results in a "boominess" that dominates, or at least interferes with faithful sound reproduction across the broad range of frequencies in the source program. Since this resonance occurs only at particular frequencies, the prior art enclosure designs have sought to eliminate the resonance completely, and rely solely on the source program and amplifying and equalization equipment to obtain an improved sound reproduction at low frequencies. See U.S. Pat. No. RE 31,483 (Hruby). It would be desirable to take advantage of the tendency to develop low frequency resonance to reinforce and enhance the reproduction of low frequency source material.